The invention relates to keys for manually operated work-holding chucks, sometimes referred to as lathe chucks.
The jaws of a lathe chuck are usually adjusted, either in turn or simultaneously, by means of a key having a spindle with a square end which can be plugged into one of a number of adjusting screws flush with or recessed into the periphery of the chuck body. The user of the key will generally apply the required torque to the adjusting screw, or to each adjusting screw in turn, with the key in an upstanding or generally upstanding position and although he will usually remove the key from the chuck as soon as he has either slackened or tightened an adjusting screw or screws there is the danger that the key can sometimes by inadvertence be left in position on the chuck. If the machine is then restarted, the key will be thrown outwards from the chuck by centrifugal force. This is, of course, a very serious hazard. A further and equally dangerous hazard is that an operator can trap his hand between the key and the machine bed if he starts up his machine whilst still holding the key in engagement with one of the adjusting screws.
According to the invention, there is provided a key for a work-holding chuck, the key having resilient means whereby it is ejected automatically from the chuck when released by the user, the resilient means being constituted by a spring steel plate member having a central hole through which a spindle part of the key freely extends and having finger elements which are deflected as the driving end of the spindle is plugged into an adjusting screw of a work-holding chuck, the spindle part of the key being provided with a loosely fitted sleeve so that a user of the key can grasp the sleeve in one hand and spin the key with his other hand. The spring steel plate member may abut against an end of said sleeve and be retained in abutment with the end of the sleeve by a circlip engaging a groove in the spindle part, and an end of the sleeve remote from the spring steel plate member may abut against a washer which in turn abuts against a circlip engaging a groove in the spindle. On the other hand, the spring steel plate may be located between a pair of circlips. A tommy bar which is provided for imparting a torque to the key may be fixed to the spindle part or may be slidably located in a hole in the spindle part through which it extends.